1. Field of the Invention
The present invention relates to the field of the energy storage devices, and, in particular, to a complete electrical energy storage and recovery system via controlled storage and discharge of kinetic energy.
2. Description of the Prior Art
U.S. Pat. No. 5,614,777 issued on Mar. 25, 1997 to Jack G. Bitterly et al, discloses and claims a flywheel based energy storage system using an integral motor/generator, high speed flywheel, and magnetic bearings. The system disclosed in the '777 patent is costly since composite rotor materials are required, does not allow for minimum power, and an active thrust bearing is required to provide the necessary force to lift the rotor and maintain levitation for active axial position control. Further, the patented system does not allow for a large motor/generator to provide high power discharges for short durations due to the nature of the construction with the motor/generator located outboard of the bearings where increasing the size would cause significant operational rotordynamic problems. In essence, although the system disclosed in the '777 patent provides advantages over prior art designs, the system cost significantly reduces its commercial viability.
What is desired therefore is to provide a low cost system suited for high or low power discharges that uses a magnetic bearing which enables passive active lifting of the rotor mass in a vertical system for minimum bearing power, thereby maximizing system efficiency.